Interpretive Summary: Airblast sprayers can be a significant source of spray drift. They pose a greater risk than ground applications because they deliver spray horizontally and vertically towards a target area. Several factors including weather conditions, crop canopy and sprayer setup can contribute to airblast spray drift. Droplet size is the most important factor in determining the potential for drift. Smaller droplets improve coverage but are more likely to be blown through or above a canopy. ARS research has shown that air induction nozzles can be used in place of conventional nozzles for reducing drift without significantly reducing coverage. Tower-type of liquid and air delivery systems significantly reduce the amount of material pushed above the top of the canopy. Cross-flow and wrap-around sprayers can reduce drift by directing spray horizontally, which keeps the spray closer to the ground. Matching the air delivery system for the desired travel speed and the target canopy characteristics will help provide enough energy to move spray droplets into the canopy and limit further downwind movement. Electronic technology that detects the absence of a canopy in front of the nozzles also reduce the amount of drift above canopies that have significant variability in height or gaps between adjacent plants. Live barriers outside of a treatment area can also reduce drift as do canopies within a treatment area but they do not necessarily eliminate the risk of drift. Operators that are aware of the limits of their machines and optimize the sprayer operation for the canopy being treated as well as sensitive sites around the treatment area will significantly reduce off-target contamination.

Technical Abstract:
Airblast sprayers can be a significant source of spray drift because they deliver spray horizontally and vertically towards a target area. Several factors including weather conditions, crop canopy and sprayer setup can contribute to spray drift. Droplet size is the most important factor in determining the potential for drift. Smaller droplets improve coverage but are more likely to be blown through or above a canopy. Large-droplet air-induction nozzles have been shown as means for reducing drift without significantly reducing coverage. Tower-type of spray and air delivery systems can significantly reduce the amount of material pushed over the top of the canopy. Cross-flow and wrap-around sprayers can reduce drift by directing spray horizontally, which keeps spray closer to the ground. Matching the air delivery system for the desired travel speed and the target canopy characteristics will help provide enough energy to move spray droplets into the canopy and limit further downwind movement. Electronic technology that detects the absence of a canopy in front of the nozzles also reduce the amount of drift over canopies that have significant variability in height or gaps between adjacent plants. Live barriers outside of a treatment area can also reduce drift as do canopies within a treatment area but they do not necessarily eliminate the risk of drift. Minimizing the number of sprays needed through IPM techniques is a non-technological means of reducing the risk of spray drift. Most importantly, operators should be aware of the limits of their machines and optimize the sprayer operation for the canopy being treated as well as sensitive sites around the treatment area.